There is known a planetary gear device provided in a vehicular power transmitting system and having a carrier which rotatably supports pinions held in engagement with a sun gear and a ring gear and which is accommodated within a casing. Patent Documents 1 through 3 disclose examples of such a planetary gear device. In the planetary gear device of Patent Document 1, the carrier is merely fitted in the casing, and is not completely fixed to the casing, so that the carrier rotatably supporting pinion gears held in engagement with the ring gear formed in an inner circumferential surface of a cylindrical output member is inclined due to a reaction force received from a counter drive gear held in engagement with a radially outer gear of the cylindrical output member, giving rise to a drawback of uneven load distribution of the pinion gears due to the inclination of the carrier, which causes generation of vibrations and noises.